It is possible to sometimes have a null PermissionBubbleManager.

chrome/browser/content_settings/permission_context_base.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/content_settings/permission_context_base.h"
 
 #include "base/logging.h"
 #include "base/prefs/pref_service.h"
 #include "chrome/browser/content_settings/permission_bubble_request_impl.h"
 #include "chrome/browser/content_settings/permission_context_uma_util.h"
@@ skipping 107 matching lines @@
   }
 
   PermissionContextUmaUtil::PermissionRequested(
       permission_type_, requesting_origin);
 
   if (PermissionBubbleManager::Enabled()) {
     if (pending_bubbles_.get(id.ToString()) != NULL)
       return;
     PermissionBubbleManager* bubble_manager =
         PermissionBubbleManager::FromWebContents(web_contents);
-    DCHECK(bubble_manager);
+    // TODO(mlamouri): sometimes |bubble_manager| is null. This check is meant
+    // to prevent crashes. See bug 457091.
+    if (!bubble_manager)
+      return;
     scoped_ptr<PermissionBubbleRequest> request_ptr(
         new PermissionBubbleRequestImpl(
             requesting_origin, user_gesture, permission_type_,
             profile_->GetPrefs()->GetString(prefs::kAcceptLanguages),
             base::Bind(&PermissionContextBase::PermissionDecided,
                        weak_factory_.GetWeakPtr(), id, requesting_origin,
                        embedding_origin, callback),
             base::Bind(&PermissionContextBase::CleanUpBubble,
                        weak_factory_.GetWeakPtr(), id)));
     PermissionBubbleRequest* request = request_ptr.get();
@@ skipping 92 matching lines @@
   DCHECK_EQ(requesting_origin, requesting_origin.GetOrigin());
   DCHECK_EQ(embedding_origin, embedding_origin.GetOrigin());
   DCHECK(content_setting == CONTENT_SETTING_ALLOW ||
          content_setting == CONTENT_SETTING_BLOCK);
 
   profile_->GetHostContentSettingsMap()->SetContentSetting(
       ContentSettingsPattern::FromURLNoWildcard(requesting_origin),
       ContentSettingsPattern::FromURLNoWildcard(embedding_origin),
       permission_type_, std::string(), content_setting);
 }